The present invention relates to a supply device for a machine working cardboard sheets, comprising at least one conveyance unit for the conveyance one by one of said sheets, driving means for these conveyance units, at least one hold-down stop of a pile of said sheets above said conveyance units and at least one raising unit connected to each conveyance unit, these raising units being alternatively movable between two restricted positions, one position above the upper level of said conveyance units, the other one where they are lightly aligned according to this upper level.
Such known devices, that is to say the ones described in patents CH-424 448 and CH-493 396 are generally used for the sheet by sheet infeed of cardboard blanks in folder-gluers. The pile of cardboard blanks is alternatively raised and lowered so that the bottom of this pile travels from a level located above the conveyance units to a level located nearly at the upper level of these conveyance units, engaging thus alternatively the lower blank of the pile with the conveyance units intended to feed the folder-gluer with these blanks one by one.
The raising mechanisms of these known devices are controlled either by cam or pneumatic cylinder. These actuating mechanisms are connected to a cradle supporting all raising units, so that the latter are travelling according to one and single movement while raising the pile simultaneously and indistinctly on its whole surface. However, when the shapes of the blanks from which their respective lengths of the various parts into the conveying direction of these blanks strongly vary, i.e. in case of blanks of boxes with covers, the simultaneous rising of all the parts of the blank is not adapted. Thus, when the body of the box leaves the conveyance units, it is necessary to prevent the box of the next blank from engaging with these conveyance units by raising it, but on the contrary, the blank part including the cover still remains thus under the pile, so that it has to remain engaged with the conveyance units until it is released from the pile. The known devices are obviously not intended to deal with this problem, so that in case of blanks like the abovementioned ones, the latter seem to be turning instead of remaining well-aligned in the axis of the conveyor belts.
The aim of the present invention is to overcome at least partly the abovementioned disadvantages.
To this end, the present invention relates to a supply device for a machine working cardboard sheets wherein the conveyance of a cardboard sheet is selectively controllable by rising units that either keep the sheet off the conveyance device or permit it to settle on the conveyance device at the appropriate time. A plurality of rising units are spaced across the conveyance direction. Each rising unit may pivot up and down above the conveyance unit. Upward pivoting of a rising unit prevents contact between a blank and a conveyance unit, and lowering the unit or the arm to or below the height of the conveyance unit permits the contact that causes the sheet to be conveyed. Selective operation of different ones of the sets of the conveyance units by an appropriate control assures that an irregularly shaped blank will be contacted by a conveyance unit at the appropriate times and not be contacted prematurely by a conveyance unit which might cause the blank to turn. There is a set of shoes at each of the conveyance units areas that are operable periodically above the respective conveyance unit to reestablish a correct top height of the rising unit, as the shoe wears, during repeated use.
Thanks to this device, it is possible to differentiate the moving of each pair of rising units according to the geometry of the blank to be feeded into the folder-gluer. The conveyance of these blanks is thus improved; the latter remain well-aligned compared to the transport axis. This device also ensures to put out of operation the rising units of the conveyance units which would be outside the pile of blanks. This permits the increase of the security and the decrease of the use of compressed air as well as the noise decrease. The conductor is able to store the various mechanisms of the rising units according to the sorting of these mechanisms and the geometry of the blank(s) to be feeded into the folder-gluer.
These advantages are more particularly profitable to three kinds of blanks, first of all to the 4-corner blanks for which the device according to the invention permits a more regular starting rate of the blanks.
The second kind of 6-corner blanks is appreciably similar to the first said one for which the advantages of the device according to the invention are the same.
The third kind of blanks profitting of these advantages are the so-called xe2x80x9ccrash-lock bottom blanksxe2x80x9d, that is to say the box blanks for which the bottom of the box itself is automatically shaped at the time of the setting into volume, and in particular the disproportionate crash-lock bottom blanks with covers for which the device of the invention permits the decrease of the phenomenon of setting in skew the blanks at the starting time.
Lastly, the device of the invention allows considering many up-to-date unknown possibilities, such as the simultaneous control of several blanks or of one blank and its reinforcement.